Swift Array GroupBy

Swift SequenceType GroupBy

extension Sequence {
	
	func groupBy<G: Hashable>(closure: (Iterator.Element)->G) -> [G: [Iterator.Element]] {
		var results = [G: Array<Iterator.Element>]()
		
		forEach {
			let key = closure($0)
			
			if var array = results[key] {
				array.append($0)
				results[key] = array
			}
			else {
				results[key] = [$0]
			}
		}
		
		return results
	}
}

// Usage

var users: [User]
users.gourpBy { $0.age }

Updated code for swift 3